1. Field of the Invention
The present invention relates to a capillary electrophoretic instrument having a capillary array assembly comprising a plurality of capillaries and, more particularly, to a capillary electrophoretic instrument (hereinafter referred to as an electrophoretic instrument) suitable for use in such as a DNA sequencer (a DNA base sequence analyzer) for analyzing samples of living organism, especially through the use of a plurality of capillaries or minute passages as a medium of electrophoretic separation, and to a capillary array assembly used in the instrument.
2. Description of the Prior Art
In the base sequence determination of DNA having a very long base sequence, a shift is occurring from a conventional flat-plate gel method, in which a gel is sandwiched between two glass plates and DNA, which is a sample, is caused to migrate electrophoretically by applying a voltage across both ends of the glass plates, to a capillary electrophoretic instrument, in which a gel is filled in capillaries made of quartz (hereinafter referred to as capillaries) and a sample is caused to migrate electrophoretically by applying a voltage across both ends of the capillary array assembly.
The above capillary electrophoretic instrument, which permits high-speed and high-sensitivity analyses in comparison with the flat-plate gel method and is less affected by the Joule heat from self-heat generation by a migration current, can provide a good resolution for an electrophoretic analysis.
In recent years, in order to increase the number of analyses per unit time allowed in one electrophoretic instrument, electrophoretic instruments in which a multiple of capillaries are set and the DNA analyses of a multiple of samples can be simultaneously performed have been coming into widespread use.
In many of these instruments, as a method for applying a voltage to the sample loading side of each capillary during sample loading into capillaries or during electrophoresis, a sample plate in which samples are set and a buffer tank for electrophoresis themselves are made of a conductor, such as a metal, or electrodes are embedded in the sample plate and buffer tank.
As in the art described in JP-A-10-206382, there is also a method in which an electrophoretic instrument has such an electrode structure that an electrode covers the area surrounding the sample loading portion of each capillary and electrophoresis is performed by applying a high voltage to the electrophoretic instrument via a wiring pattern connected to each electrode.
In the above-mentioned technique in which the sample plate and buffer tank for electrophoresis themselves are made of a conductor such as a metal, an analyst must have ready a large number of sample plates having a voltage application structure peculiar to each DNA analyzer as mentioned above for the NDA analyses of a large number of samples. This has posed the problems of increased running costs related to analyses and increased burden oh analysts.
Next, it is desirable that a general-purpose microtiter-plate, etc. is capable of being used in an electrophoretic instrument. Of course, however, this microtiter-plate is not provided with an electrode portion capable of being connected to the electrophoretic instrument. For this reason, a technique for incorporating electrodes in an electrophoretic instrument cannot be used.
Furthermore, in an electrophoretic instrument which has an electrode structure portion covering the area surrounding the sample loading portion of each capillary and is provided with a wiring pattern connected to each electrode structure portion and to which a high voltage is applied, the capillary replacement work is very troublesome.
In addition, capillaries have a short life and in some applications it is necessary to perform analyses by resetting capillaries of different lengths. On this occasion, an analyst must set a multiple of capillaries one after another in the electrophoretic instrument, posing the problem of much expense in time and effort.
Further, in this method, in order to load a sample into the capillaries, cylindrical electrodes are beforehand brought into contact with the sample in the sample plate, and then by driving and moving the sample plate, the above capillaries are inserted into the cylindrical electrodes, thereby to bring the capillaries into contact with the sample. Therefore, in order to simultaneously insert a plurality of capillaries with an outer diameter of several hundreds of micrometers into cylindrical electrodes, extremely high accuracy must be required of a driving portion of the sample plate or the cylindrical electrodes must have an inner diameter with a sufficient allowance.
When accuracy is given to the above driving portion by reducing the diameter of the cylinder of above electrode, a sample measured last time remains in a gap between the inner surface of the cylindrical electrode and the outer surface of the capillary due to the capillary phenomenon, posing the problem that a good-accuracy electrophoretic analysis is impossible.
When accuracy is not required of the driving portion by increasing the diameter of the cylinder of the electrode, the possibility of mixing of other samples due to the above capillary phenomenon decreases. However, this case poses the problem that because of the large diameter of the electrode, the bottom end of the electrode does not reach the well bottom of the sample plate with such an inverted cone shape that the well becomes narrower toward the bottom.
Because the bottom end of above electrode does not reach the well bottom, it does not come into contact with a sample or a buffer solution, with the result that in principle, sample loading and electrophoresis are impossible. Therefore, in a case where the electrode is to be brought into contact with the above sample and buffer solution and a general-purpose microtiter-plate is to be used, a minimum amount of sample must be set at a large value in order to raise the liquid level of the sample and buffer solution, thus posing another problem.
The present invention was made in order to solve these problems with the prior art. Accordingly, a first object of the present invention is to provide a capillary electrophoretic instrument that reduces running costs related to analyses and burdens on analysts, facilitates the replacement work and setting of capillaries, permits good-accuracy analyses, and enables minimum amounts of sample to be set at small values.
A second object of the present invention is to provide a capillary array that reduces running costs related to analyses and burdens on analysts, facilitates the replacement work and setting of capillaries, permits good-accuracy analyses, and enables minimum amounts of sample to be set at small values. According to an embodiment of the present invention, there is provided a capillary electrophoretic instrument which comprises: a capillary array assembly comprising a capillary array having a plurality of capillaries each of which has a bore for containing a separation medium and forming an electrophoretic lane, each of which has a sample loading port at one end thereof and a sample detection port remote from the sample loading port; a plurality of electrodes each of which is so disposed as to form a pair with the each of the capillaries at the position near the sample loading port; an electroconductive member, connected to a power source, for electrically connecting the plurality of electrodes; and a capillary array holder for holding the capillary array, the electrodes and the electroconductive member, a plurality of sample holders for holding a sample to be analyzed, each of which is located at a position corresponding to each of the pairs of said capillaries and the electrodes, and a sample moving table for moving sand supporting the plurality of sample holders.
Further, according to another embodiment of the present invention, there is provided a capillary array assembly that comprises: a capillary array, which has a plurality of capillaries forming electrophoretic lanes and constituting a sample loading port at one end thereof and a sample detection port remote from the sample loading port; and a capillary array assembly, which has a plurality of electrode members installed to form a pair with each of the above plurality of capillaries in the above sample loading port, an electroconductive member electrophoretically connected to the above plurality of electrode members and connected to a power supply for applying a voltage to the above capillary array, and a capillary array holder for holding the above capillary array, electrode members and electroconductive member.
There is provided, as a first aspect of the present invention stated in claim 2, a capillary electrophoretic instrument that comprises, at least; a sample plate having a plurality of wells for housing a sample; a buffer tank for housing a buffer solution for effecting electrophoresis; and auto sampler on which the above sample plate and buffer tank are placed; a plurality of capillaries which are each filled with a gel and which are each inserted into each of the above wells and are brought into contact with the sample thereby to absorb the sample and are also brought into contact with the buffer solution thereby to form an electrophoretic lane; a plurality of electrode members each installed in the vicinity of the above plurality of capillaries; an electroconductive member which comes into electrical contact with the above plurality of capillaries; a capillary array holder for integrally holding the above plurality of capillaries, the above plurality of electrode members and the above electroconductive member; a power source for applying a voltage across the loading end and trailing end of the above capillary; and a controller for controlling the above auto sampler and the above power source.
The capillary electrophoretic instrument of the above construction is briefly explained.
In order to reduce burdens on analysts, the construction of the capillary electrophoretic instrument permits the use of a commercially available microtiter-plate and the sample plate and buffer container are not given an electrode structure.
The electrode portion for applying a voltage to the capillary is integrally formed with the capillary array so that the electrode portion can be attached to the capillary electrophoretic instrument and detached therefrom. This eliminates troublesomeness during capillary setting.
As the above electrode portion, there are disposed metal wires in the vicinity of the capillaries at minute intervals, for example, at distances of about 1 mm, parallel to the relevant capillaries.
Further, the above capillaries are inserted into the cylindrical electrodes having almost the same inner diameter as the outer shape of the capillaries, and the above electrodes and capillaries are bonded to each other so that a gap through which other samples mix in is not formed.
Further, in the above capillaries, the electrode portions are formed by vapor-depositing a thin metal film or an electroconductive material on outer walls of the capillaries.
The above means permits the use of a commercially available, inexpensive microtiter-plate, etc. as the sample plate, enables a capillary array of capillaries, which have a long life and must be replaced according to the nature of an analysis, to be simultaneously set, eliminates troublesomeness, and permits stable DNA analyses by preventing the mixing of other samples.